Wave guide and its method of manufacture

ABSTRACT

A WAVEGUIDE FOR THE TRANSMISSION OF ELECTROMAGNETIC WAVE ENERGY WHICH IS MADE OF A STEEL PIPE HAVING A COPPER METAL LAYER FORMED BY COPPER PLATING ON THE INNER SURFACE OF THE PIPE, AND EXTREMELY THIN SEMI-ELECTROCONDUCTIVE LAYER DISPOSED ON THE COPPER METAL LAYER BY MEANS OF ELECTRO CHEMICAL TREATMENT OR CHEMICAL TREATMENT AND A UNIFORM DIELECTRIC LAYER STEADILY ADHERED TO THE SURFACE OF THE SEMIELECTRO CONDUCTIVE LAYER AND METHODS OF MANUFACTURING IT.

. Feb. 23,'1-971 s SAWADA ET AL 6,566,316

WAVE GUIDE AND ITS METHOD OF MANUFACTURE Filed Nov. 24, 1967 INVEN R 4 $0M/a' AWAOT 5 H/easu/ SIl/OYAMA BY 7Isuusa NAmHA/ew 5 6 I 72/5/19 Arranucvs CA eofuses (wear/{52s United States Patent 01 3,566,316 Patented Feb. 23, 1971 ice 3,566,316 WAVE GUIDE AND ITS METHOD OF MANUFACTURE Sumio Sawada, Nishinomiya, Hiroshi Shioyama, Ashlya,

and Tsuneo Nakahara, Nislliuomiya, Japan, asslgnors to Sumitomo Electric Industries, Ltd., Osaka, Japan, a

company of Japan Filed Nov. 24, 1967, Ser. No. 685,602 Int. Cl. H01p 11/00, 1/16, 3/12 US. Cl. 333--95 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION 1 )Field of the invention The present invention relates to Waveguide for the transmission of electromagnetic wave energy of the circular electric or TE mode and methods of manufacturing it.

(2) Description of the prior art Waveguides with dielectric inner lining of constructions as shown in FIGS. 1(a), (b) and FIGS. 2(a), (b) have already been known. In the case of the waveguide shown in FIGS. 1(a), (b), a copper plating layer (B) of a uniform thickness is formed on the inside of a round steel pipe (A) and is covered with a dielectric layer (C) of a uniform thickness.

In the case of the Waveguide shown in FIGS. 2(a), (b), it has a double lining layer, the inner surface of a round steel pipe being copper plated, an electrical lossy material layer (D) of a uniform thickness being provided thereon and a loss less dielectric layer (C) being provided again thereon.

For the production of such waveguides, a method in which an adhesive is applied to the copper plating layer and a dielectric tube of polyethylene or the like is installed, has heretofore been employed. In the case of the waveguide shown in FIGS. 1(a), (b), however, the adhesion between the copper plating layer and the dielectric (polyethylene or the like) is poor, so that it has often been the case that the dielectric layer peels 01? and causes defects. Moreover, in the case of the waveguide shown in FIGS. 1(a), (b), the transmission characteristic of the electric wave has been found to have such a shortcoming that the phase constant of the transmission mode TE and those of such unwanted modes as TE TE etc. coincide with each other at certain frequencies and the mode conversion coefiicient at those frequencies becomes large, so that the transmission loss becomes remarkably great. For instance, in the case of a waveguide of an inner diameter of 51 mm. with a polyethylene inner lining of a 0.32 mm. thickness, the TE mode has the same phase constant as the TE 31 mode at 27 gc., as the TE mode at 51 gc. and as the TM mode at 5 6 gc.

In the case of the waveguide shown in FIGS. 2(a), (b), the lossy layer (D) has a substantial thickness, and the waveguide has little influence of mode conversion as observed in the case of the waveguide shown in FIG. 1.

However, the wave of the transmission mode TE is also attenuated, as the lossy layer is relatively thick. In this case, it becomes a fatal defect for a long distance transmission.

SUMMARY OF THE INVENTION This invention relates to an improvement on the waveguide heretofore used for the transmission of electric waves of the circular electric mode or TE mode. The waveguide according to this invention has such a construction that a semi-electroconductive film of a thickness of 1-5 1. is formed on the conductor surface inside the metallic pipe which constitutes the waveguide and a dielectric layer is provided over said semielectroconductive film. Compared with a waveguide with a dielectric inner lining which has no lossy layer, the bonding is more secure because the dielectric layer is bonded to the semielectroconductive layer.

With the waveguide having a dielectric inner lining of the conventional type and a lossy layer provided for the purpose of attenuating unwanted mode waves, the thickness of the lossy layer is comparatively great, so that the transmission of electric circular mode and TE mode waves for a long distance shows a loss which is not negligible. In the case of the construction according to the present invention, however, the thickness of the lossy semi-electroconductive layer is extremely small, so that, compared with the waveguide with a dielectric inner lining of the conventional type which has a lossy layer, it has an advantage that it represses unwanted mode waves and transmits electric circular mode or TE mode waves for a long distance with little transmission loss.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 show steel pipe waveguides with dielectric inner linings heretofore in use, FIG. 3 is a schematic drawing of an apparatus embodying the first manufacturing method of the present invention, and 'FIG. 4 is a schematic drawing of an apparatus embodying a second manufacturing method of present invention.

DESCRIPTION OF THE PREFERRED EMB ODIMENTS The methods of two principal embodiments of the present invention for the manufacture of waveguides with dielectric inner linings are described below.

The apparatus for the first embodiment is shown in FIG. 3. In FIG. 3, 1 denotes a steel pipe whose inner surface is copperplated, 2 the cathode placed along the central axis of the steel pipe, 3 stoppers provided at both ends of the steel pipe for sealing in the electrolytic solution which serve as cathode rod supporters at the same time, 4 a hose for circulating the. electrolytic solution, 5 a tank for the electrolytic solution, 6 a pump for the circulation of the electrolytic solution, 7 a variable direct current source, 8 a terminal for connection with the steel pipe, 9 a terminal for connection with the cathode, and 10 the wiring from the electric power source 7 to the terminals '8 and 9.

In FIG. 3, a circulation system of electrolytic solution is formed by a steel pipe 1 forming the waveguide of the present invention which is copper plated on its inner surface, two stoppers 3, which serve as supporters of cathode which are installed at both ends of the steel pipe, three hoses which joint stopper 3 and circulation pump 6 stopper 3 and tank 5 and circulation pump 6 and tank 5, a tank for the electrolytic solution which is connected with hose 4, and circulation pump 6 for the solution which is connected with hose 4. A 10-50% solution of caustic soda kept at C.- C. fills the interior of the circulation system. An iron rod as a cathode is supported along the central axis of steel pipe 1, which functions as an anode, by means of two supporters 3 which seal in the electrolytic solution. The iron rod is connected with the negative terminal of a variable direct current voltage source 7 through the conductor and the steel pipe 1 is connected to the positive terminal of source 7 through the conductor 10. The electrolytic solution filling the circulation system is circulated by means of a pump 6 and at the same time direct current voltages are applied between the positive and negative electrodes by steps; for instance, 0.5 v. for one minute, 1 v. for three minutes and 1.5 v. for one minute.

In this way a lining of copper oxide, semi-electro conductive, having a uniform thickness of 23;/. is formed on the inner surface of the steel pipe. A dielectric layer, such as a polyethylene layer for example, is then formed to a uniform thickness by the conventional method on the inner surface of the steel pipe that has been given the copper oxide treatment as mentioned above. In the case mentioned above, it is also possible to use potassium hydroxide for the electrolytic solution.

The second embodiment of the present invention is processed in the apparatus shown in the FIG. 4.

The circulation system of treating solution of the apparatus of FIG. 4 is filled by a 10-20% solution of caustic soda with an addition of sodium chlorite heated at a temperature near 100 C. After the solution is circulated by means of a pump 6 in the circulation system for several minutes, a layer of copper oxide having a uniform thickness of about 1%, which is semi-electroconductive, is deposited on the inner surface of the copper layer of the steel pipe as a result.

Caustic potash may also be used in this case in place of caustic soda. Then the same method as that heretofore employed is used to form a dielectric layer on the inner surface of the steel pipe. The waveguide with dielectric lining having extremely thin semi-electro-conductive layer may be fabricated in such a way.

With the first and the second embodiments either the vertical or the horizontal type may be used for the copper plating of steel pipes and any of the copper cyamide baths, the copper boronfiuoride baths, the copper sulphide baths, etc. may be used. If the process of forming a copper oxide film by cutting open the bath after this final process is employed, there will be an advantage in that the manufacture can be carried out very easily.

The waveguide obtained in this way has a very strong adhesion. Even if the solution collects in a pit existing on the surface of the steel pipe, it is stable because of the caustic soda and is thus free from the hitherto experienced shortcoming whereby scaling off takes place. For instance, if a Waveguide with an inner lining is immersed in water or put in a similar condition of high humidity, scaling-off takes place in about one week in the case of waveguides heretofore in use. It has been found, however, that waveguides made according to the present invention remain free of scaling-off for 4 weeks or more. With respect to transmission characteristics, the mode conversion loss from the main transmission mode TE to spurious modes is small because of the loss property of the very thin semi-electroconductive layer on the surface of the copper plating layer, so that there will be no interference for a wide range of frequencies. Also, as the semi-electroconductive layer is exceedingly thin, a waveguide with a dielectric inner lining which is stable may be obtained, the loss of the main transmission mode TE wave being little. The waveguide is thus particularly excellent for a long distance transmission line.

According to the present invention, an embodiment in which the inner surface of a steel pipe is copper-plated and a thin semi-electroconductive layer of copper oxide is formed and a dielectric layer is formed thereon has been described. However, the same effect will be obtained also by forming a very thin semi-electroconductive layer or a very thin layer of a high loss property (for example,

4 chromic acid film, phosphoric acid film, molybdenum film, lead oxide or a sulphide such as copper sulphide, etc.) on the surface of a Waveguide and coating it with a dielectric layer.

We claim:

1. A waveguide comprising a metallic pipe, a copper plating layer plated on the inner surface of said pipe which constitutes the main body of the waveguide, a film of metal oxide having a thickness of about one to five microns formed continuously on said copper plating layer, and a dielectric layer adhered to said film of metal oxide.

2. A waveguide comprising a metallic pipe, a copper plating layer plated on the inner surface of said pipe which constitutes the main body of the waveguide, a film of metal sulfide having a thickness of about one to five microns formed continuously on said copper plating layer, and a dielectric layer adhered to said metal sulfide film.

3. A method of manufacturing a waveguide having a dielectric inner lining comprising the steps of providing a waveguide having a copper inner surface as an anode, providing a cathode along the axis of the waveguide, filling the space between these electrodes with a 10-50% solution of caustic soda, maintaining said solution at a temperature of C. to boiling point, applying voltages by steps to the electrodes to form a copper oxide film, and adhering a dielectric layer on said copper oxide film.

4. A method of manufacturing a waveguide with a dielectric inner lining comprising the steps of circulating a l20% aqueous solution of a strong alkali with an addition of the chloric acid salt of an alkali metal and kept at 80 C.boiling point in a waveguide having a copper inner surface to form a copper oxide film on the copper surface, and adhering a dielectric layer on said copper oxide film.

5. A waveguide comprising a tube having an electro conductive inner surface and a dielectric layer on said electroconductive surface and characterized by a semielectroconductive film of a type chosen from the group consisting of metal oxides and metal sulfides and of about one to five microns thickness formed on said conductive surface, said dielectric layer being closely adhered to said semi-electroconductive film.

6. The method of manufacturing a waveguide comprising the steps of providing an elongated tube having an electroconductive inner surface, treating the inner surface of electroconductive material to chemically produce a semi-electroconductive film selected from the group consisting of chromic acid film, phosphoric acid film, molybdenum film, metal oxides and metal sulfides and having a thickness of about one to five microns, and adhering a dielectric layer to the surface of the semielectroconductive film, wherein the step of treating the electroconductive lnner surface includes the steps of mounting an elongated cathode in a spaced insulated relation from the electroconductive inner surface and along the longitudinal center of the tube for the full length thereof, filling the interior of the tube between the cathode and the electroconductive inner surface with an electrolytic solution capable of electrochemical reaction with the electroconductive surface to produce the semi-electroconductive film, heating the electrolytic solution to a temperature in the range of eight degrees centigrade to the solution boiling point and maintaining the solution temperature in this range, electrically connecting the positive terminal of a variable direct current voltage source to the electroconductive inner surface and the negative terminal thereof to the cathode, and controlling the variable voltage source to apply voltages by steps.

7. The method of manufacturing a waveguide compr1s1ng the steps of providing an elongated tube having an electroconductive inner surface, treating the inner surface of electroconductive material to chemically produce a semi-electroconductive film selected from the group consisting of chromic acid film, phosphoric acid film, molybdenum film, metal oxides and metal sulfides and having a thickness of about one to five microns, and adhering a dielectric layer to the surface of the semielectroconductive film, wherein the step of treating the electroconductive inner surface includes the steps of circulating through the electroconductively coated tube a solution capable of chemical reaction with the electroconductive inner surface to form the semi-electroconductive film, heating the solution to a temperature Within the range of eighty to one-hundred degrees Centigrade, and maintaining the temperature of the solution Within this range.

8. The method of manufacturing a Waveguide comprising the steps of providing an elongated tube having an electroconductive inner surface, treating the inner surface of electroconductive material to chemically produce a semi-electroconductive film selected from the group consisting of chromic acid film, phosphoric acid film, molybdenum film, metal oxides and metal sulfides and having a thickness of about one to five microns, and adhering a dielectric layer to the surface of the semi-electroconductive film.

References Cited UNITED STATES PATENTS 3,078,428 2/1963 Miller 333 '95 OTHER REFERENCES Round Waveguide With Double Lining, Unger, in Bell 0 System Technical Journal, January 1960, pp. 161-167.

15 ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner US. Cl. XLR. 29-600; 333--98 

